This invention relates in general to reproduction apparatus in which copy sheets carrying unfused images are moved successively along a path through a heated fuser. More particularly, this invention relates to thermal conservation apparatus for minimizing the loss of thermal energy from a heated fuser along the copy sheet path.
In reproduction apparatus such as electrographic apparatus, unfused toner images of originals are generally formed on copy sheets which are moved successively through the electrographic apparatus and which are permanently fused by means of a heated fuser through which the copy sheets are passed. A heated fuser creates problems within the electrographic apparatus because of the heat produced. Since the fuser may be located closely to the photoconductive member, heat from the fuser may undesirably change the imaging characteristics of the photoconductive material. Copy sheet transport apparatus such as vacuum belts located before or after the fuser also tend to draw heat away from the fuser. Since a heated fuser may be the largest consumer of power within electrographic apparatus, it has been found desirable to conserve the thermal energy of the fuser as much as possible. Such conservation techniques have included the use of insulated covers which confine the heat within the fuser. Such covers are shown, for example, in U.S. Pat. Nos. 3,998,584; 3,937,919; and 3,667,742. In order to gain access to the fuser, the cover may be moveable such as shown in U.S. Pat. No. 3,356,831 and Research Disclosure No. 16732 dated March 1978, entitled "Thermal Conservation Assembly for Roller Fuser," (published by Kenneth Pobl. Ltd., Hamphine, U.K.). Such conservation assemblies are still not effective in preventing the escape of heat along the path of the copy sheets. It has been proposed in U.S. Pat. No. 3,849,907 to provide fusing apparatus in which copy sheet curl is reduced by means of brush-like seals adjacent the fusing zone for limiting air flow at the fusing zone. It has also been proposed in German Pat. No. 2,321,837 to provide at the entry to and exit from a heated fixer, fireproof shutters which are held by heat-sensitive wires which melt when the heat inside the fixer exceeds a safe level so that the shutters intersect the copy sheet path and isolate the fixer. These shutters are not selectively moveable into and out of the copy sheet path however.
It would thus be desirable to provide a heated fuser in which thermal energy is conserved by minimizing the loss of thermal energy from the fuser along the path of the copy sheets in order to prevent overheating of adjacent components such as a photoconductor and to reduce the amount of energy consumed by the heated fuser. Such conservation apparatus is especially desirable during warm-up and stand-by and during intervals between copy sheets. However, it would also be desirable to inhibit the conservation apparatus when successive copy sheets are spaced closely together to facilitate movement of sheets through the fuser.